When fabricating a spectacle lens having an edged lens shape complying with the frame shape of a spectacle frame by grinding the circumferential surface of an unprocessed round lens (to be also referred to as an uncut lens or a processing target lens hereinafter), if the lens is held with a weak force, the processing resistance applied by a grinding stone may cause axial deviation of the lens. More specifically, the processing center position of the actual lens may deviate from the lens rotating shaft. The axial deviation of the lens appears in a direction (radial direction) perpendicular to the processing center position when the lens does not have a cylinder axis, and includes deviation in the direction perpendicular to the processing center position and deviation in the rotational direction with respect to the processing center position when the lens has a cylinder axis. To solve this problem, conventionally, various methods have been proposed such as increasing the lens holding force, or employing an edging apparatus, an edging method, and an adhesive tape as described in Japanese Patent Laid-Open Nos. 2003-300138, 11-333684, 11-333685, 2002-182011, and 2004-122302.
The lens processing method and processing apparatus described in Japanese Patent Laid-Open No. 2003-300138 improve the processing accuracy of the circumferential surface of a lens without requiring in advance the design data of the lens to be finished. Hence, according to this lens processing method, the processing target lens is roughly processed based on the lens frame shape data of a spectacle frame or shape data that can comply with a spectacle, and thereafter the shape of the lens is measured. Then, the lens is finished to a shape complying with the shape of the spectacle frame or a shape complying with the spectacle based on the rough processing shape data obtained by the measurement.
The spectacle lens processing apparatus described in Japanese Patent Laid-Open No. 11-333684 processes a lens highly accurately by preventing axial deviation, breaking of the lens, and coat cracking. For this purpose, this spectacle lens processing apparatus includes a first lens chuck shaft on which a processing target lens is mounted through a fixing cup, a second lens chuck shaft which is arranged coaxially with the first lens chuck shaft and on which a lens retaining member to retain the processing target lens is attached, a rotational deviation detection means for detecting the deviations of the rotation angles of the lens chuck shafts, and a process control means which processes the processing target lens based on the detection result obtained by the rotational deviation detection means.
The spectacle lens processing apparatus described in Japanese Patent Laid-Open No. 11-333685 allows processing a processing target lens under appropriate conditions in accordance with the shape of the lens under processing. To achieve this, according to the spectacle lens processing apparatus, an encoder provided to a servo motor detects the travel amount (the shaft-to-shaft distance between a lens chuck shaft and the rotating shaft of a grinding wheel) of a carriage. An obtained detection signal is sent to a controller. The controller measures the during-processing shape corresponding to the rotation angle of the lens from an input signal. The processing pressure (the preset value of the rotary torque) is changed to correspond to the during-processing shape. More specifically, when the lens chuck shaft is distant from a processing end portion, the process is started after decreasing the processing pressure by lowering the carriage. As the distance to the processing end decreases, the processing pressure is increased gradually. When the processing pressure is changed depending on a lens processing diameter in this manner, axial deviation can be suppressed, and highly accurate processing can be performed.
According to the technique described in Japanese Patent Laid-Open Nos. 2002-182011 and 2004-122302, a double-coated adhesive tape or a coating film is formed between a processing target lens and a lens holding means, so that slipping is prevented.